The present invention relates to an information recording medium and, more particularly, to an information recording medium in which digital information such as computer data or a digital audio signal can be recorded in real time with a recording energy beam such as a laser beam or an electron beam.
As such an information recording medium, a recording medium in which information is recorded using a difference between the reflectances of an amorphous phase and a crystalline phase with respect to a laser beam is used. For example, when a laser beam is irradiated on a recording thin film whose initial state is a crystalline state, the irradiated portion is rapidly heated and cooled, and the state of the irradiated portion is changed into an amorphous state, thereby forming a mark which is different from a non-irradiated portion in reflectance. In addition, when a laser beam weaker than that used in the recording operation is irradiated on the mark formed in the recording medium, this irradiated portion is moderately heated and cooled, and the amorphous state of the mark formed portion is returned to the crystalline state which is the initial state.
As the material of such a recording thin film in which phase transition between an amorphous phase and a crystalline phase can be reversibly performed, in other words, a recording thin film in which a recording operation and an erasing operation can be reversibly performed, an alloy consisting of Sb and Te or an alloy consisting of Ge, Sb, and Te and obtained by improving the characteristics of the alloy consisting of Sb and Te is known.
Although the alloy consisting of Sb and Te is crystallized within a short time, the amorphous state of the alloy is not satisfactorily stable. In the alloy consisting of Ge, Sb, and Te, the component ratio of Ge must be set to be 10% or more to obtain a satisfactorily stable amorphous state. However, in this case, a long time is required to crystallize the alloy. In addition, with the progress of an information-oriented society, a higher transmission speed of information and better durability for holding recorded information are demanded. However, as a temperature at which an amorphous phase is changed into a crystalline phase is higher, the durability for holding recorded information in the recording thin film described above becomes better. However, the alloy consisting of Sb and Te and the alloy consisting of Ge, Sb, and Te pose the above problems, and do not completely satisfy the above demands.